1. Field of the Invention
The present invention relates, in general, to the powder metallurgy production of metallic implements and components by hot isostatic pressing (HIP) of powder and, more particularly, to the powder metallurgy production of metallic implements and components by HIP plus wrought processing after consolidation. The present invention further relates to powder metallurgy production of metallic implements from a Nitinol alloy for service requiring properties such as high hardness and corrosion resistance.
2. Description of Related Art
Nitinol is an intermetallic compound of nickel and titanium which was serendipitously discovered at the Naval Ordinance Laboratory by W. J. Buehler in 1959. One of the Nitinol compositions (Ni-40Ti weight percent) has unique properties that cannot be found in other materials. This composition can be heat treated to a hardness of Rockwell C 60 or higher and is wear resistant and non-galling even though it has a high titanium content. In addition, although it has a high nickel content, it is non-magnetic. It is also highly corrosion resistant in a variety of media. The density is 86 percent of the density of steel which is advantageous in applications where weight is a consideration. This composition also has superelastic and shape memory properties.
Even though this composition has a number of attractive properties, it has not seen significant usage because it is a difficult composition to process by the common metallurgical practice of ingot melting followed by hot and cold working. This composition in cast form can be brittle and can crack unexpectedly under otherwise normal processing conditions. Several attempts have been made to manufacture implements with this composition using an ingot metallurgy or investment casting approach. However, due to the difficulties in conventional ingot metallurgy processing of this composition it has not been widely used.
Accordingly, a need exists for an improved process for producing implements and components from the Ni-40Ti composition that overcomes the deficiencies of using an ingot metallurgy or investment casting approach.